Computing devices, such as notebook computers, personal digital assistants, mobile communication devices, portable entertainment devices (e.g., handheld video game devices, multimedia players) may include user interface devices that facilitate interaction between a user and the computing device.
One type of user interface device that has become more common operates by way of capacitance sensing. A capacitance sensing system may include a touch screen, touch-sensor pad, a touch-sensor slider, or touch-sensor buttons, and may include an array of one or more capacitive sensor elements (also referred to as sensor electrodes). Capacitive sensing typically involves measuring, through sensor signals (e.g., increases or decreases in electrode responses), a change in capacitance associated with the capacitive sensor elements to determine a presence of a conductive object (e.g., a user's finger or a stylus) relative to the capacitive sensor elements.
Changes in capacitance are measured across arrays of sensors when they are used for sensing and processing capacitive touch applications. Because the “changes” are measured, changing information (AC or delta information) is desired in order to detect variation in capacitance, while constant information (DC or signal offset) is not desired. The DC component is rejected. The term “baseline” refers to the offset, or base capacitance that is already present on a sensor. The challenge is how to detect what the baseline is for one or more sensors and efficiently remove the baseline from the received signal while conditioning the remaining signal for further processing (e.g., determining if an object is in a specific location on a capacitive sensor array). Current methods to address this issue are both complex and inefficient, and not always effective.